多项选择题

A. A main query can have more than one subquery.B. A su……

Which three statements about subqueries are true? （）

A. A main query can have more than one subquery.
B. A subquery can have more than one main query.
C. The subquery and main query must retrieve data from the same table.
D. The subquery and main query can retrieve data from different tables.
E. Only one column or expression can be compared between the subquery and main query.
F. Multiple columns or expression can be compared between the subquery and main query.

<上一题目录下一题>

热门试题

单项选择题For which action can you use the TO_DATE function? （）

A. Convert any date literal to a date
B. Convert any numeric literal to a date
C. Convert any character literal to a date
D. Convert any date to a character literal
E. Format '10-JAN-99' to 'January 10 1999'

单项选择题What is true regarding subqueries?（）

A. The inner query always sorts the results of the outer query
B. The outer query always sorts the results of the inner query
C. The outer query must return a value to the outer query
D. The inner query returns a value to the outer query
E. The inner query must always return a value or the outer query will give an error

单项选择题What is true about sequences? （）

A. The start value of the sequence is always 1.
B. A sequence always increments by 1.
C. The minimum value of an ascending sequence defaults to 1.
D. The maximum value of descending sequence defaults to 1.

单项选择题Examine the structure of the EMPLOYEES table: EMPLOYEE_ID NUMBER Primary Key FIRST_NAME VARCHAR2 (25) LAST_NAME VARCHAR2 (25) HIRE_DATE DATE Which UPDATE statement is valid? （）

A. UPDATE employees SET first_name = 'John' SET last_name = 'Smith' WHERE employee_id = 180;
B. UPDATE employees SET first_name = 'John', SET last_name = 'Smoth' WHERE employee_id = 180;
C. UPDATE employee SET first_name = 'John' AND last_name = 'Smith' WHERE employee_id = 180;
D. UPDATE employee SET first_name = 'John', last_name = 'Smith' WHERE employee_id = 180;

单项选择题Examine the statement: Create synonym emp for hr. employees; What happens when you issue the statement? （）

A. An error is generated.
B. You will have two identical tables in the HR schema with different names.
C. You create a table called employees in the HR schema based on you EMP table.
D. You create an alternative name for the employees table in the HR schema in your own schema.